1/2 c. butter
1 c. brown sugar, packed
1/4 c. milk
1 3/4 - 2 c. powdered sugar

Melt butter, add brown sugar. Boil over low heat 2 minutes, stirring constantly. Stir in milk. Heat until it comes to a boil. Cool to lukewarm. Add powdered sugar. Beat well. If too thick, add a little hot water.